The present invention relates generally to motor control systems, and more particularly, to motor control center subunits having a remote disconnect system which governs the connection of motor control components to supply power. In one embodiment, the system and method described herein provides for the connection and/or disconnection of supply power to the motor control components via the control of a subunit circuit breaker from a remote location.
A motor control center is a multi-compartment steel enclosure with a bus system to distribute electrical power, on a common bus system, to a plurality of individual motor control units mountable within the compartments. The individual motor control center subunits are commonly referred to as “buckets” and are typically constructed to be removable, pull-out units that have, or are installed behind, individual sealed doors on the motor control center enclosure. These buckets may contain various motor control and motor protection components such as motor controllers, starters, contactor assemblies, overload relays, circuit breakers, motor circuit protectors, various disconnects, and similar devices for electric motors. The buckets connect to the supply power lines of the motor control center and conduct supply power to the line side of the motor control devices, for operation of motors. Motor control centers are most often used in factories and industrial facilities which utilize high power electrical motors, pumps, and other loads.
Typically, the motor control center units are monitored and controlled on-site by an operator. The operator controls the activation of subunits in the motor control center and may, for various reasons (e.g., a system alert), elect to open or close a circuit breaker/unit disconnect so as to connect and/or disconnect supply power to the subunit. For motor control center starter units, an actuation of the unit disconnect does not automatically energize the motor circuit. Instead, the energizing of the motor circuit is controlled via a remote computer or communications protocol.
In “feeder” motor control center units, however, such actuation of the unit disconnect acts to energize the motor circuit. In existing “feeder” motor control center designs, it has been necessary for the operator to manually turn a disconnect handle, which operates the circuit breaker/unit disconnect control switches to control such connection and disconnection. Once activated, the switches control a number of individual switching mechanisms within the circuit which ultimately open or close the circuit. By tripping the circuit, power distribution can be managed. The manual operation of the disconnect handle, however, requires that an operator be located in the vicinity of the motor control center. Thus, it may be necessary for the operator to travel back and forth to the motor control center to manually actuate the disconnect handle. Furthermore, manual actuation of the disconnect handle also necessitates that the operator put on protective gear so as to be shielded from potential arc flash events that can occur, as is known in the art. The putting-on and removal of such protective gear can be time consuming and the need for the operator to be in proximity to the motor control center to manually actuate the unit disconnect is highly undesirable.
While the use of a shunt trip is possible for remotely actuating (i.e., opening) the circuit breaker/unit disconnect, the use of shunt trips shortens the life of the circuit breaker. That is, while shunt tripping may be a practical means for opening the circuit breaker remotely, use of a shunt trip results in the need for the breaker to be cycled through a reset action. Additionally, use of the shunt trip to repeatedly open the circuit breaker increases wear on the circuit breaker, as such mechanisms are typically designed for only 10% shunt trip operation.
It would therefore be desirable to design a motor control center bucket assembly that overcomes the aforementioned drawbacks. A control mechanism and a remote device that allows for remote connection or disconnection of the circuit breaker, without the use of a shunt trip, would be beneficial, by providing a more efficient and cost-effective system for controlling a motor control center unit circuit breaker.